Teletypewriter selective calling and switching system



Nov. 11, 1941. R. J. ANSPACH 2,262,541

TELETYPEWRITER SELECTIVE CALLING AND SWITCHING SYSTEM Filed June 14,1959 5 Sheets-Sheet l SIGNAL RELEASE BUSY FIG. I

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A T 7019/ /E V NOV. 11, 1941; J ANSPACH $262,541

TELETYPEWRITER SELECTIVE CALLING AND SWITSHING SYSTEM F-iled J'dne i4,1939 '5 Sheets-Sheet 4 FIG. #4

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TELETYPEWRI'IEER SELECTIVE CALLING AND SWITCHING SYSTEM Filed June 14,1939 5 Sheets-Sheet 5 60/ MON ITORING 77 LOCAL CEfl IIRAL OFFICE I //vl/ENTOR RJ. ANSPACH ATTORNEY Patented Nov. 11, 1941 A, 2,262,541 ENT[OFFICE TELETYPEWRITER SELECTIVE CALLING AND SWITCHING SYSTEM RussellJacob Anspach, Westfield, N. L, assignor to America n Telephone andTelegraph Company, a corporation of New York Application June 14, 1939,.Serial No; 279,190

14 Claims.

This invention relates to a teletypewriter selective calling andswitching system having pullbar-operated contacts for effecting callingand switching operations and, more particularly, to

such a system having improved means forfeffecting supervisoryoperations; I

Accordingly, itis an object of this invention to provide the system withmeans operating in response to a preassigned permutation code signal tocause a busy signal to be set up at all subscribers, stations in thesystem other than the calling subscribers station, for rendering thelocal motor start mechanism, at these stations ineffective, and also forconditioning the selective calling and switching apparatusfor operationuIt is also an object of the invention to provide the system with meansoperating in response to another preassigned permutation code signal todisable the selective calling and switching apparatus after the desiredcalling and. switching functions have been performed and to conditionthe system for thetransmissionof messages.

A further object of, the invention is to provide the system with meansfor restoring the system to its normal condition, after the transmissionof a message, in response to the transmission of certain preassignedpermutation code signals.

, A modification of the invention hasfor its object the insuring ofprivacy of communication by insuring that the loop extending from a:subscribers station to a central ofiice will, after the subscriber hasoperated hisstart key, be conditioned on a one-way basis, the directionbeing from the subscribers station tothe central ofiice, and will not beconvertedto a two-way basis until the signal assigned for selecting thatstation has been transmitted.

These and other objects of the invention are accomplished by means of asystem employing teletypewriters of the typedisclosed in Patent1,745,633. granted February 4, 1930 to S. Morton et al. The disclosureof this Morton et aLpatent is incorporated herein by reference as apartof this specification. These teletypewriters are located at subscribersstations and are equipped with control contacts some'of which areoperated by the pullbars in the teletypewriters and some by otherapparatus in the teletypewriters, such as by the platen shift mechanism,in the manner described. in Patent 2,120,235, granted June 14. 1938 toJ. F. Beattie et al. The disclosure of this Beattie et a1. patent isincorporated herein by reference as a part of this specification. Eachcentral ofiice in the system is provided with a monitoringteletypewriter which is equipped with control contacts of the type justdescribed.

When a subscriber wishes to connect his teletypewriter to that atanother subscribers sta tion for the purpose of communicationtherebetween, he applies ground to the midpoint between the operatingwindings of two polarized H (01. 178-2) relays.

. above.

,This IGVGISGStht-l polarity of the ourthe, tip side of the loop to thecalling station and extendsthe subscribers loop circuit to the maintransmission channel through all the central offices inthe system whichserves to start the calling subscribers-teletypewriter motor, ring hisbell and lighthis busy lamp. The subscriber then transmits a;figures+shift signal which effects as a preparatory condition theapplicationof ground to pull-bar operated conrent in trol contactslocated in monitoring teletypewriters at alli the central ofiices. Henext transmits a preassigned permutation code signal, su'ch'as A, whichsets up a busy signal at all the other subscribers. stations connectedintothe system and renders their local motor start mechanisminefiective. It also causes a guard lamp to be lit at the callingsubscribers station and serves to condition the selective callingapparatus for operation.

The calling subscriber then transmits another preassigned permutationcode signaLg such as B, which connects the called subscribers loop into.the circuit, causes the selectedcalled subscribers motor tobe started byremote control and alsoeiiects anaudible calling signal. This isfollowedqby another preassigned permutation code signal, such asfC,transmitted from the calling station which serves to extinguish theguard lamp at the ,callingsubscribers station and also temporarilydisables the selective calling, arrangement. i

After the subscriber has completed his communication, he can disconnectthe communicative connection by transmitting a shift signal followed bythe signal for A and then another preassigned permutation code. signal,such as (D). same functions atfthistime as was describedTheDzsignal,causes the motor control circuit to be opened therebystopping the motor at both the called subscribers station and thecalling subscribers station It'also efiects the extinguishment of theguard lamp at the disconnecting station which became operated inresponse to the transmission of the A signal, and causes the busy lampsat all stations to be extinguished. The circuitis thus restored to itsnormally unoperated condition.

Int he modification of the invention whereby privacy of communication isassured, the operation of the start key at a subscribers station willcondition the subscribers loop, extending from that station to. acentral office, on a one-way basis, the direction being. from thesubscribers station to the central oflice. This one-way loop is notconverted toa two-way basis until the signal assigned for selecting thatstation has been transmitted. After t eloop has beenconverted to atwo-way basis, communication takes place in the manner described above.Since none The shift and the A signals perform the.

2 of the loops extending from the subscribers stations can be placed ona two-way basis until the signals assigned for selecting them have beentransmitted, it is impossible for any subscriber not connected into theparticular communicative connection to eavesdrop.

These and other features of the-invention are fully described inconnection with the .Ifollowing detailed description of the drawings, inwhich:

Figure 1 represents three subscribersteletypewriter stations located atone end of the system and shows in detail the apparatus and circuitconnections at two of the stations, it being understood that the thirdstation is similarly q pp d;

Fig. 2 illustrates switchingrelays and circuit connections at theteletypewriter central oflice nearest the subscribers stations shownin'Fig. 1;

Fig. 3 shows similar apparatus and circuits at a distant teletypewritercentral oflice;

Fig. 4 ilustrates three subscribers teletypewriter stations, two indetail and one schematically, located at the distant'end of the system;

Fig. 5 indicates the relationship of the apparatus and circuits shown inFigs. 1, 2, 3, and 4 to the system as an entirety; and

Fig. 6 shows a teletypewriter central oflice similar to the centralofiice shown in Fig. '2 but which is provided with means for insuringsecrecy of communication by preventing the loops extending from thesubscribers stations shown in Fig. 1 to be connected to the centraloffice of Fig. '6 on a two-way basis until the signals-assigned forselecting them have been transmitted.

In Fig. 1, a typical subscribers teletypewriter station 'IOI is shown tobe provided with a teletypewriter I02, similar to the teletypewriterdisclosed in the Morten et al. patent mentioned above, having areceiving magnet I03, sending contacts I04, and break key I05 connectedinto a communication channel I06 extending to the local central ofiice20I shown in Fig. 2. Teletypewriter I02 is equipped with ,pullbars I01,I08, and I09 adapted to operate a plurality of control contacts III, H2,and H3 in the manner described in the Beattie et al. patent mentionedabove. Another control contact H is operated by a bell crank II4 whichis a part of the mechanism used to shift the platen from lower case toupper case and vice versa in the manner described in the Beattie et al.patent.

A source of alternating current H is supplied to operate the subscribersrectifier H6 and motor 1. Station IOI is further provided with .a bell,or ringer, 8, a non-locking, manually operable start and signalreleasekey I I9, a guard lamp I2I, and a busy lamp I22. It is .also providedwith an auxiliary stop key I20 .for use particularly with the secrecyfeature to be described hereinafter.

Of all the relays atstation IOI, only two are normally energized. Theseare the polarized relays I23 and I24 which are normally energized bytheir local biasing .circuit to hold the armature ofrelay I23 on itsmarking contact and the armature of relay I24 on .its spacing contact.Negative current in the tip circuit will hold the armature of relay I23on.its marking contact and positive current will move the armature toits .spacing contact. Likewise, negative current in the ring circuitwill hold the armature of relay I24 on its spacing contact and positivecurrent will move it to its marking contact. During business hours, thesubscriber the motor control relay I21.

Station IOI has a loop I06 extending to the .local central ofiice 20Iwhich is provided with a monitoring teletypewriter 202, similar to theteletypewriter described in the Morton et al. patent mentioned above,and a telegraph repeater 203, which may be of any suitable construction.Since both the repeater 203 and the monitoring printer 202 are connectedinto the main'communication line 204 leading to the distant centralofiice 30I, printer 202 runs continuhours. Mounted in teletypewriter 202above the pullbars 205, 206, 201, 208, and 209 are control contacts 2II,2I2, 2I3, 2I4, and 2I5 which are designed to be operated by the pullbars205 to 209, inclusive, in the manner described in the Beattie et al.patent mentioned above. Contact 2I0 is operated by a portion 2I6 of theshift mechanism in the manner described in the Beattie et al. patent.

Central 'office 20I is provided with a separate set of switching relaysfor each local outlying teletypewriter station in the selective callingand switching system that has a communication channel, similar tochannel I06, leading to central ofiice 20L In each set of switchingrelays, all of the relays are normally unenergized except polarizedrelay 2II which is normally energized by current from battery 239passing over its local biasing circuit to hold its armature on itsmarking contact. Positive current in the operating winding of relay 2 ITwill hold its armature on its marking contact and negative current willmove the armature to its spacing contact.

The ring side'R of line I06 is connected over the inner bottom armatureof relay 2I8 to negative grounded battery 2I0. The tip side T of lineI06 is connected through the operating winding of relay 2II, over theinner top armature of relay 2I8, and over the inner top armature ofrelay 220 to negative grounded battery 22I. As batteries '2I9 and 22Iare of equal and like polarities, no current will flow in thesubscribers loop I06 to station IOI at this time which is the normalidle condition.

When the subscriber at station IEII desires to originate a call to someother station in the system, he manually operates his non-locking startand signal release key' II9 thereby applying ground I28 to his loop at apoint midway between the operating windings of polarized relays I23 andI24, Negative current from battery 2I9 will now travel over the ringside R of loop I06 and through the operating winding of relay I24 toground I28. Negative current from battery 22I will pass through theoperating winding of relay 2II and then over the tip side T of line I06and through the operating winding of relay I23 to ground I28. As thedirection of this current flow is such as to aid the current normallypassing from rectifier I I6 through the biasing windings of relays I23and I24, the position of the armatures of relays I23 and I24 is notchanged.

However, at the central office 20I, the flow of negative current throughthe operating winding of relay 2 I1 causes the armature of relay 2I'I tobe moved to its spacing contact thereby closing a path for currentfromgrounded battery 222 ously during business I 2,262,541, to passthroughthe winding 01 relay 223, 'over thearmature of relay 2I'I to ground 224.This causes relay 223 to operate, its armatures. The

inner armature of relay 223 completes a shortcircuit path across thewindings of relays 2I0 and 229. This shunt path extends from battery225, over the top armatureof relay 220, and then over theinner armatureof relay 223 to ground The outer armature of relay 223 closes a path forcurrent from grounded battery 225 to pass through the winding of relay220 and over the outer armature of relay 223' to ground 226 i therebyenergizing relay 220 whichoperates its armatures and locks up over itsbottom armature and over the armature of relay 221 to ground 228. Theoperation of 5 the inner toparmature of relay 220 switches the tip side,T of, line I06 from negative battery 22I to, positive battery 230. Theoperation of the outer top armature of relay 220,

opensfythe short circuit across the windings of relays 2I8 and 1229. I r

Accordingly, current from battery 225 willnow operate theirxarmatures,the calling subscribers circuit is extended to repeater 203 and the maincommunication channel 204. Negative current from the tip output terminalof repeater 203 will now pass over the tip side of loop I06, through theoperating winding of relay I23, and then over the top part of start keyI I 9 to ground I28, This causes relay I23 to move its armature to itsmarking contact thereby extinguishing busy lamp I22.

At the same time, positive currentfrom the ring output terminal ofrepeater 203 will pass through the monitoring teletypewriter 202, overthe ring side R of thecalling subscribers circuit, through the operatingwinding of relay I24, and then over the top part of key III! to groundI28. This causes relay I24 to move its armature to its marking contactto permit current from the posipass through the windings of relays 229and 2I8 typewriter 202and repeater 203 at central oilice 20I and thenout over line 204 to the distant centraloffice 30I. The operation of theinner top armature of relay 2I8 disconnects battery 230 from1 the tipside T, of line I06 and the operation of theouter top. armature of relay2I8 connects this side of line I06 to the other side of the maincommunication circuit, leading through repeater 203 and out over line204. H

Thus, the subscribers; circuit, is extended through the monitoringteletypewriter 202 and the telegraph repeater 203 at thelocal centralofli ce 20I, out over the main transmission line 204 to the distantcentral oilice 30I, through the, repeater 303, and the monitoringteletypewriter 302. At the same timefthebottom armature of relay 229closes a shuntpath across the operating winding ofrelay 2I'I thereby, ineffect, remove ing its inductance from the subscriber's loop. Thiscauses relay 2 H to move itsarmatureback to its marking contact therebyopening the energizing circuitof relay 222 which releases its armatures.I i i When the inner top armature of relay220'was operatedto switch thetip side T of line I 06 from negative battery 22I to positive battery230 and before relays 229 and 2 I8 became energized, positive currentfrom battery 230 passed over the tip side T of the subscribers loop I06for a brief period of time. This current flow is of short durationbecause relay 2I8 soon operates its armatures to switch thesubscribersloop I 66 from battery 230 to the main line 204. However, this temporaryfiowof current in the tip side of loop I06 merely causes the subscribersrelay I23 to move its armature momentarily to its spacing contact tomomentarily light the busy lamp I22 over a circuit to be tracedhereinafter. H

When relays 229' and 2 IBbecome energized and tive terminal of thesubscribers rectifier II6 to pass through the winding of relay I29, overthe armature of relay I24 and its markingcontact, through the winding ofmotor control relay I21, Winding of relay I30, and their over the toparmature and contact of slow-release relay I3I to the negative terminalof rectifier II6 thereby energizing relays I21, I29, and I30 whichoperate their arinatures. The operation of the top armature of relay I29closes a path for'current to pass from the r positive terminal ofrectifier II6, through ringer 30;

I I0; and then over the top armature of relay I29 to the negativeterminal of rectifier II6. This serves to operate the subscribersaudible signal device, ringer I113. The operation of the bottom armatureof relay I29 does not accomplish any useful function atthis time becausethe path leading from the bottom contact of relay I29 is open at thelower part ofkey II9 due to the subscriber holding this key open now inorder to make his call. i I

Control relay I 27 operates its armature to close the energizing circuitfrom the source II5 of alternating current through the subscribers motorII I therebystarting motor III. Relays I30 and I21" lock up'over a pathleading from.

the positive terminal of rectifier H6, over the inner top armature ofrelay I30, through the windings of relays I21 and I30, and then over thetop armature of relay I3I to the negative terminal of' rectifier II6.Consequently, relay I21 remains energized and maintains its arma-' tureoperated to keep the energizing circuit of motor II'I closed. l

At the same time, the operation of the bot-' tom armatureof relay I30closes a path for current to pass'fromthe positive terminal of rectifierH6, over the bottom armature of relay 2 I30, through busy lamp I22, andthen back to the negative terminal of rectifier H6. This serves tooperate the calling subscribers visible signal device, busy lamp I22.

I The operation of the outer top armature of relay I30 closes a shuntpath from the ring side R, of the line I06 over the outer top armatureand contact of relay I30 to the subscribers receiving magnet I03 therebyshort-circuiting the operating windings of relays I23 and I24. Whenrelays I23 and I24 are shunted out of the loop, the current in theirbiasing windings holdstheir armatures in the positions shown in Fig. 1.Consequently,-the armature of relay I 24 is moved to its spacing contactthereby opening the energizing circuit of relay I29 which releasesitsarmaturesto discontinue the operation of ringer H8. As theshort-circuiting of the operating windings er relays I23 and I24 occursvery shortly after relay I29 was energized, the operation of ringer I! 8is so brief that it is hardly more than a momentary operation.

The starting of motor N1, the brief ringing of hell H8, and the lightingof busy lamp I22 all indicate to the subscriber at station I! that histeletypewriter I02 is now connected into the main communication circuit204 in communicative relation with both the monitoring teletypewriter262 at the local central oflice and the monitoring teletypewriter 302 atthe distant central office 30! and is ready for operation.

For the sake of simplicity, the main communication channel is shown toextend between only two central oifices 20! and 30!. It is to beunderstood that, if desired, it may include other teletypewriter centralofiices and that the channel may be of any suitable type. Accordingly,the subscriber releases his start and signal release key H9 and proceedsto establish the desired communicative connection.

The subscriber at station I!!! now transmits a figures-shift signal toeffect the shifting of the platen in his teletypewriter I02 to its uppercase position in the manner described in the Beattie et al. Patent2,120,235 mentioned above. This causes the operation of the bell cranklever H4 to close the platen contact H0 which remains closed until aletters-shift signal is transmitted. The manner in Which this platencontact I I0 is operated is described in the Beattie et a1. patent.Closure of platen contact IIO activates the pullbar contacts III, H2,and H3 by connecting them to the positive terminal of rectifier II6.This figures-shift signal is also received by the monitoringteletypewriters 202 and 302 at the central offices 20! and 30! andeffects the operation of bell cranks H6 and 3I5 to close the platencontacts 2I0 and 3I0. This activates the pullbar contacts 2!! to 2I5,inclusive, by applying to them ground 23!, and also activates pullbarcontacts 3!! to 3I5, inclusive, by applying to them ground 33!.

Next, the subscriber at station I0! transmits a so-called preparesignal, such as the permutation code signal for A. Other signals may bepreassigned for use instead of A if desired and it is to be understoodthat this is the case with other specific signals to be mentionedhereinafter and that the specific designation of A and other lettershereinafter is set forth for the purpose of this description and thatthe invention is not limited to the use of only these particular codecombinations. This A signal is received by all the teletypewritersmonitoring on the circuit and causes each of them to operate the properpullbar to momentarily close the A pullbar contact.

Thus, at central ofiice 20!, pullbar 205 is operated to close contact2!! to complete a path for current to pass from grounded battery 232,through the winding of relay 233, contact 2, and then over the platencontact 2!!) to ground 23! thereby energizing relay 233. Relay 233 nowoperates its armatures and locks up over its top armature, armature ofrelay 234, and then over the armature of relay 22'! to ground 228. Theinner bottom armature of relay 233 prepares an energizing circuit frombattery 235 through relay 22'! but this circuit is left open at the Dpullbar contact 2I2. The outer bottom armature oi relay 233 connectsground 236 to the contacts of relays 231, 254, and 214. The middlebottom armature of relay 233 closes a path for current from batteries225, 255, and 215 to pass through the windings of relays 220, 250, and210, respectively, and then over the middle bottom armature of relay 233to ground 236.

As was described above, relay 226 has already operated its armatures tolock up over its bottom armature and over the armature of relay 22'! toground 228. Relays 250 and 210 now operate their armatures to lock up ina similar fashion. The operation of the inner top armature of relay 250switches the tip side of loop I56 from negative A battery 25! topositive battery 253 and the operation of the outer top armature ofrelay 250 opens a short circuit across the windings of relays 256 and251. This causes current to flow over loop I56 in such a direction as tocause the polarized relay I5! at the subscribers station I34 to move itsarmature to its spacing contact thereby closing a path for current fromthe subscribers rectifier I to energize busy lamp I52. The subscribersstart key I59 is rendered ineffective due to the positive current in theoperating winding of relay 258 at central ofiice 20! which holds thearmature of relay 258 on its marking contact. Likewise, the operation ofthe armatures of relay 210 effects a similar flow of current in loop II6which accomplishes the lighting of the busy lamp at the subscribersstation I6! and disables the start key at station I6! in a mannersimilar to that described above.

At the same time, pullbar 305 at the distant central oflice 30! isoperated to close contact 3!! to effect the energization of relay 333.Relay 333 operates its armatures to perform the same functions as relay233 and causes the energization of relays 320, 350, and 310 whichoperate their armatures and lock up over their bottom armatures and thearmature of relay 32'! to ground 328. The operation of inner top.armature of relay 320 switches the tip side T of the loop 406 extendingto the subscribers station 40! from negative battery 32! to positivebattery 330. At the same time, the operation of the top armature ofrelay 320 opens a short circuit across the windings of relays 3I8 and329.

Since the tip side T of the subscribers loop 406 now has positivecurrent from battery 330 and the ring side R still has negative currentfrom battery 3I9, current will now flow over the subscribers loop 406.However, in the normal oper- I ating condition of the circuit duringcommunication, negative current is applied to the tip and positivecurrent to the ring. Consequently, the current now in the subscribersloop 406 is flowing in a direction which is the opposite of the normalmarking loop current used during communication.

The positive current from battery 330 now flowing in the tip circuitcauses polarized relay 423 at station 40! to move its armature to itsspacing contact. This closes a path for current from the positiveterminal of the subscribers rectifier 4 I 6 to pass over the armatureand spacing contact of relay 423, through the busy lamp 422, and thenback to the negative terminal of rectifier 4 I 6. Consequently, thesubscribers indicator, lamp 422, becomes operated to provide thesubscriber at station 40! with a visual indication that anothersubscriber in the system is making a calling selection.

The local motor starting mechanism at station 40! is renderedinefiective because operation of the subscribers start and signalrelease key 4I3 will now be of no effect as it is in a state equivalentto being disabled. This is due to the fact that positive current frombattery 330 is now on the tip circuit extending through the operatingwinding of relay 3" and merely assists in holding the armature of relay3 I 1 on its marking contact. Consequently, operation of start key M9 atthis time will not be able to effect the operation of the armature ofrelay 3I1 to its marking contact.

Similarly, the operation of the armatures of relays 350 and 310 switches456 and 416 from negative batteries 35I and 3H topositive batteries 353and 313, respectively. This causes relay 451 at the subscribers station434 to eflect the energization of busy lamp 452. At the, same time, thesubscribers start'key 459 is rendered ineffective. Likewise, at station46I, the busy lamp is illuminated and the start key rendered ineffectiveby means similar to those described above. Thus, the transmission of theprepare signal, A, by the calling subscriber at station IOI, causes thebusy lamps at all the other subscribers stations in the system to becomeilluminated and also prevents the operation of, their start keys frombeing efiective to start their teletypewriter motors at this time.

The calling subscriber at station I M only subscriber whoseteletypewriter is connected into the system for the transmission andreception of signals. Accordingly, the transmission of the preparesignal, A, efiects the operation of the A pullbar I08 in theteletypewriter at station IM to close momentarily its contact III for isnow the closing a path from the positive terminal of recti v fier II6over the platen contact IIO, contact III, through the winding of relayI32, and then to the negative terminal ofrectifier II6 therebyenergizing relay I32. r

Relay I32 operates its armatures and locks up over its top armature,armature of relay I33, and

, then over the bottom armature ofrelay I3I to the positive terminal ofrectifier H6. The operation of the outer bottom armature of relayI32prepares an energizing circuit for relay I3I butthis circuit is leftopen at the .D The operation of the inner bottom armature of relay I32closes a path for current to pass from the negative terminal ofrectifier II6, over the innerbottom armature of relay I32,.through theguard lamp I2 I, and then to the positive terminal of rectifier II6.This causes the calling subscribers indicator, guard lamp I2I, which mayhave a red bulb, if desired, to be operated to pro-- vide the subscriberat station I0I with a visual indication that the system has now beenprepared for the transmission of a station selecting signal.

If it is found that the relays mentioned above are not sufiicientlyquick in operating, the selecting routine may be modified to requirethat the calling subscriber either transmit the prepare signal, A, twiceto allow suificient time for these relays to operate their armatures andfor the lamps to light or else pause for a brief interval of time beforetransmitting the station selecting signals. This applies also to betransmission of other permutation code signals to be hereinafter thathave been preassigned to perform selective switching and supervisoryfunctions.

The subscriber at stationv IOI, having decided which of the othersubscribers stations, such as station MI, is to be conditioned forcommunication, now transmits the proper station selecting signal, suchas.B.

the system is provided with a pullbar contactthe pullbar contact II2.

mentioned Only one teletypewriter in,

the tip sides of loops I w operation of which is effected bythetransmission of the B signal and that is the monitoringteletypewriter 302 at central oflice 30I serving station 40I.Consequently, the B, code signal effects the operation of the pullbar308 in the monitoring teletypewriter 302 which closes the B1 pullbarcontact 3I4. The closure of contact 3I4 closes a path for current frombattery 338 to pass through the-winding of relay 331, contact 3M, andthen over the platen contact 3I0 to ground 33I thereby energizing relay331.

Relay 331- operates its armature to complete the path from ground 336over the operated. outer bottom armature of relay 333, armature of relay331, and then through the windings of relays 3I8 and 329 to battery 325.This energizes relays 3I8 and 329 which operate their armatures and lockup over the top armature of relay 329 and arma- Q ture of relay 321 20'3, of loop 406 through the monitoring teletypewriter 302 to the positiveringterminal of the telegraph repeater 303 at central oflice 30Ileading'out over the main communication line 204 to the other centraloflice 20I. The operation of the inner 35 top armature of relay 3I8disconnects the tip side T'of line 406 from the battery 330 and theoperation of the outer top armature of relay 3I8 connects this side ofloop 406 to the negative tip terminal of repeater 303. Thus, thesubscribers loop 406 is extended from the subscribers station 40Ithrough the central ofiice 30I, over the main transmission line 204 tocentral oflice 20I, and then over loop I06 to the calling subscribersstation IOI.

When the inner top armature of relay 320 was operated previously toswitch the tip side T of line 406 from negative battery 32I to positivebattery 330, positive current passed over the tip side T of thesubscribers loop 406 to cause the subscribers busy lamp 422 to beilluminated as was described above. This condition continues until relay3I8 operates its armatures as described above to switch the subscribersloop 406 from batteries 330 and 3I9 to the main line 204. The normalmarking current now flows over the subscribers loop 406 from positive onthe ring to negative on the tip. This causes the armature of relay 423to be moved to its marking contact and the armature of relay 424 to bemoved to its marking contact.

The operation of the armature of relay 424 to its marking contactpermits current from the positive terminal of the subscribers rectifier4I6 to pass through the winding of relay 429, over the armature of relay424 and its marking contact, through the winding of motor control relay421, winding of relay 430, and then over the top armature and contact ofrelay 43I to the negative terminal of rectifier 4I6, thereby energizingrelays 421, 429, and 430 which operate their armaturs.

Relay 429 locks up over a path from the positive terminal of rectifier4I6 the ring side R of line 406,

through the winding of relay 429, the lower portion of the start andsignal release key 4I9, over the bottom armature of relay 429, and thento the negative terminal of rectifier 4H5. The audible signal device,ringer. M8,, is now operated by being energized by current from thepositive terminal of rectifier 4l6- passing through ringer M8 and thenover the top armature of relay 429 to the negative-terminal of rectifier416. Since relay 429 is locked up, the operation of ringer 418 will becontinued until stopped by the subscriber when he momentarily operatesthe key 4 I 9 to open the locking-up circuit of relay 429.

Control relay 42'! operates its armature at this time to close theenergizing circuit from the source M of alternating current through thesubscribers motor 4|! to start motor 4H. This energizing circuit formotor 4H is kept closed due to relays 439 and 4:21 locking up over apath leading from the positive terminal of rectifier 416, over the innertop armature of relay 430, through the windings of relays 421 and 430,and then over the top armature of relay 431 to the negative terminal ofrectifier 41.6.

The operation of the outer top armature of relay 539' closes a shuntpath fro-m the ring side R. of the line 406 over the outer top armatureand contact of relay 430 to the subscribers teletypewriter 32 therebyshort-circuiting relays 423 and 424' and causing them to hold theirarmatures in the positions shown in Fig. 4.. Also, at this time, thevisible signal device, busy lamp 422, which was extinguished when relay423 moved its armature to its marking contact, is operated by currentpassing from the positive terminal of rectifier 455, over the operatedbottom armature of relay 430, and then through the busy lamp 422 to thenegative terminal of rectifier 416.

The starting of motor 4W, the ringing of bell 418, and the lighting ofbusy-lamp 422 indicates to the subscriber at station Gill that histeletypewriter 4&2 is now connected into the main communication circuitin response to a call fromsome other subscriber in the system.Accordingly, the subscriber momentarily operates his'start' and signalrelease key 419 to unlock relay- 429 to discontinue the operationof hell4+8 andthen awaits the transmission of signals from thecallingsubscriber.

Other subscribers stations may be joined with stations tilt and 4! toform a conferenceconnection. The calling subscriber at station It)!could. establish such a conference connection by transmitting at thistime the preassigned code signalsto effect the closure of the properpullbars in the central ofiice monitoring teletypewriters serving thedesired subscribers stations, as only these particular monitoringteletypewriters will have pullbar contacts that will. beoperated inresponse to the particularv station selecting signals. Thus, at centraloffice 20.1, closure, of the pullbar contact 215. in the monitoringteletypewriter 282 will efiect the selection of the subscribers stationl34. Likewise, operation of pullbar 3.99 in the monitoringteletypewriter 302 at central. ofiice 35]! will close con--- tact M5 toefifect the. connection of. subscribers station 434.

After all the. desired subscribers stations havebeen connected forcommunication, the calling subscriber at station llll transmits aso-called go ahead signal which is some preassigned code signal, suchasv the permutation code signal for 0.. Reception. of. this signal atall central officeseffects the operation of the C pullbars 201. and.3.01tomomentarily operate the C contacts 21-3- and; 34-3. 7 Operation of.contact 213 at central office 2% closes apath from battery 240, throughthe winding of relay 23.4 thereby energizing relay. 234 which monientarily-v operates its armature tolopen the locking-up circuit ofrelay 23.3.

Accordingly, relay 233 releases its armatures tov open the directenergizingv circuits of relays 27ft, 250', and 213.. However, relays22.0, 259, and 21B. remainl'ocked up over their bottom armatures. andthe armature of relay 22.7 to ground 2285. Operation of" contact 313 atcentral office 34H likewise eifects the momentary energization of relay3.34 to perform functions similar to those of relay234 while relays320,356, and S'F'EJ'remain locked up; Since relays 220, 253; 2'50, 323',350, and 370' remain energized; and locked up, the busy lamps at all theuncalled subscribers stations in the system are kept illuminated and thei start keys at these stations remain disabled. as described above.

At thecalling subscribers station let, the transmission of the C signalwill cause the momentary operation of pullbar I01 which will momentarilyclose the C contact H3 to close a path from the positive terminal ofrectifier l l6, over contacts Hlland M3, through the winding of relayI333 and then to the negative-terminal of. rectifier. H8thereby-energizing relay I33. Relay l:3-3 operates its armature to openmomentarily thelocking-up circuit of relay I32 which releasesitsarmatures. The release of the inner bottom armature of relay I32opens the energizing circuit of guard lamp I21 which, accordingly;. isextinguished.

This. conditions the apparatus at station I!!! for communicativepurposes and two-way communication may now be had between the callingstation HH- and. the called station 46! or any other selectively called.stations that may be con-- nected into aconference connection. The onlyrestriction on this communication is that thepermutationcodecombination, such as A, that has beenzv preassigned to serve as a.prepare signal mustnot be; used. in ordinary communication whenever theplatens of the teletypewritersare in. their upper case-position Whenthepurposesof this communication. connection. have been accomplished and itis desired. to. return. the system to its normal. idle condition, thesubscriber at station it transmits a figures shift signal to effect theclosure of the platen. contacts in all the operating tale-- typewritersin the system to activate the pullbar contacts as these pullbar contactswere-deactivatediwhemduring the course of communication, a letters-shiftsignal was transmitted to open the platen contacts. The subscriber atstation I01 follows this, with the prepare signal, which issomepreassi'gned permutation code signal; such as Af.

Transmission of this, signal causes the A pullbar contacts 2 and 3H atcentral offices" 2M and" 301 to be momentarily closed to effect.

the energization of relays 233 and 333. Relays 23-3 and 333 operatetheir armatures and look.

up to' performthe functions described above. addition, this signal will"effect the momentary closure of pullbar contacts Ill and 4H at stationsHI! and 40! to cause relays I32 and 432 to become energized. Relays 32and 432 operate their armaturesand lock up to perform the functionsmentioned above. Similar functions are performed at each of the, othersubscribers stationsconnected into the conference connection.

I circuit. The release of the bottom I The subscriberat station. I0| nowtransmits the disconnect signal, such as D, which has beenpreassigned toeffect the operation of pullbars I09 and 409 for closing momentarilycontacts IIZ and H2. The disconnect signal D, uponbeing receivedatcentral oflice I, causes the D pullbar, 206 to be actuated to operatemomentarily contact 2I2. This closes a path for currentgto pass. frombattery 235, through the windingof relay221, over the inner bottomarmature of relay 233,- over contact 2I2,\ and then over the platencontact 2I0 to ground 23I thereby. energizing relay 221. Relay22Ijoperates its armature to remove ground 228 from the locking-upcircuit of relays 220,. 229, 2I8, and 233, thereby causing relays 220, 229, 2I8, and 2 33 and any similar relays at central oflice 20I, suchas;relays 250,. 256, and 251 that might have been energized forestablishing a conference connection, to releasetheir armatures. Thisextinguishes the busy lamps at stations I34 and IN and also removes .thedisability from the start keys at these stations. The transmission ofthe disconnect signal D eiTects similar operations at the distantcentral office 30I.

At station l0l, closure of the D pullbar contact II2 closes a path forcurrent fromthe positive terminal of rectifier '6 to pass over contactsI I0 and ..II2, over the outer bottom armature of relay I32, through thewinding of slowrelease relay I3l, and then to the negative terminal. ofrectifier II6 thereby energizing relay I3I which operates its armatures.The operation of the top armature of relay I 3| opens thelocking-uprcircuit of relays. I30 and I21 and causes these relays torelease their armatures. The release of the outer [top armature of relayI30 opens theishunt path across relays I23 and IE4 to switch them,in.effect,, back into the line armature of relay I30 extinguishes thebusy lamp I22 by opening its energizing circuit. The release of thearmature of relay 'I2I opens the'energizing circuit of the subscriber'smotorII'land causes it to stop. Operationof the bottom armature .ofrelay I3I opens the locking-up circuit of relay I32 which, consequently,releases its armatures to open the circuit to the guard lamp I2I and theenergizing path of relay I3I Relay I3l releases its armatures inaccordance with the time delay inherent in its slow-releasecharacteristic.

229 and 2H3, will release their armatures before relay I3I releases itsarmatures; This precaution' is necessary because otherwise thesubscribers motor I I! might be unintentionally restarted dueto thearmatures of relays 229 and H8 not yet being released. The transmissionof thedisconnect signal D station 40I' and all effects similaroperations at other connected subscribers stations, thus restoring thesystem to its normal is assumed, for illustrative purposes, to be localto the subscribers stations IOI, I34, and I6I shown in Fig. 1. Thedistant subscribers? stations may be considered to be the stations MI,434. and NI shown in Fig. 4 and it is to be understood that the centralofiice to which they are connected has beenmodlfled to resemble centraloflice 60l and" that-the main line 604 extends This time delay insuresthat the relays at the central oifice 20I, especially relays from.theflmonitoring teletypewriter 602 and telegraph repeater 603 atcentral office GM to a similar telegraph repeater and monitoringteletypewriter at the distant central oilice; In the idle condition ofthe system the subscriber's loop I06 has its tip side connected tonegative battery I and 6I6- operate their armatures and lock up over thetop armature of relay 629, outer armature and contact of relay 634, andthen over the armature of relay 621 to ground 626.

The operation of the inner top and inner bottom armatures of relay 6I8disconnects the subscriber's loop I06 from batteries 630 and 6| 9. Theoperation of the outer top armature of relay 6I8 transfers the tip sideof loop I 06 over the topcontact. of relay 66I, .through the upperwinding of polarized relay 662, and then to grounded negative battery663. The operation of the outer bottom armature of relay 6I8 transe fersthe ring side of loop I06 over the inner bottom. contact of relay 66I togrounded positive battery 664.

w The subscribers loop I06 now has negative current from battery 663flowing over the tip side of loop I06 through the operating winding ofpolarized relay I 23 to ground current from battery 664 flowing over thering side of loop I06 through the operating winding of relay I24 toground I 28. Consequently, relay I23 holds its armature on its markingcontact and relay I24 operates its armature to its marking ,contact.

AsWas described above, subscribers teletypewriter motor 1, rings hisbell II8 briefly, and lights his busy lamp I 22, all of which indicatesto the subscriber at station I 0I that the system is now conditioned forthe monitoring teletypewriters, such as the monitoring teletypewriter602, at all the central offices in the system to receive signalstransmitted from the subscribers teletypewriter I02. Such signals willcause the armature of relay 662 to move back and forth between itsspacing andmarking contacts to open the circuit leading through themonitoring teletypewriter 602 to the ring and tip terminals ofrepeater603 which will in turn repeat the signals out over the main transmissionchannel 604 to the other central oiiices and their monitoringteletypewriters.

However, although the subscriber at station IOI can now transmit signalsover the main line 604, the system is in a condition such that thesubscribers teletypewriter I02 cannot receive any signals transmittedfrom any other teletypewriter in the system. This is because the circuitextending from the ring terminal of repeater 603' passes through themonitoring teletypewriter 602, over the armature of relay 662, innerbottom contacts of relay 660, top contacts of relay 660, along conductor680, through the other sets of switching relays at central office GM,and then to the tip terminal of repeater 603. Thus,

this starts the calling call, the subscriber at station I 28 andpositive the subscribers loop I08 is conditioned on a oneway basis, thedirection being from the subscriber to the central oflice, and anysignals now passing over the main line 604 and through the centraloili-ce circuit just traced cannot be received by the teletypewriter I02at station Illl.

The subscriber at station Hll now transmits a figures-shift signal toactivate the pullbar contacts in his teletypewriter and in all themonitoring teletypewriters in the system. The subscriber then sends aprepare signal, such as A, which, at central office 6M, causes pullbarcontact ill I to close a path for current from battery 632 to energizerelay 633 which operates its armatures and locks up over its toparmature, inner armature of relay 634, and armature of relay 521 toground 628. This prepare signal also performs its other functions asdescribed above, such as effecting the closure of pullbar contact HI toenergize relay I32 which operates its armatures to illuminate the guardlamp I2l.

The calling subscriber next transmits the permutation code signal, suchas X, that has been preassigned to convert his loop I06 to a two-waybasis. Only one teletypewriter in the system 'is provided with a pullbarcontact the operation of which is effected by the transmission of the Xsignal and that is the monitoring teletypewriter 632 at central ofliceGUI serving station IOI. Consequently, the X code signal effects theoperation of the pullbar 698 in the monitoring teletypewriter 602 whichcloses the X pullbar contact 6H1. Closure of contact 6M closes a pathfor current from battery 638 to pass through the winding of relay 631,contact 614, and then over the platen contact 610 to ground 63! therebyenergizing relay 631 which operates its armatures.

The operation of the bottom armature of relay E231 closes an auxiliaryenergizing circuit for relays 629 and M8 over the outer bottom ofarmature relay 633 to ground 636. The operation of the top armature ofrelay 631 closes a path for current to pass from battery 665 through thewinding of relay 66L over the top armature of I relay B31, and then overthe outer bottom armature of relay 33 to ground 636 thereby energizingrelay 56!. Relay BBI now operates its armatures and locks up over itsouter bottom armature and the armature of relay 621 The operation of thetop armature and inner bottom armature of relay B6! closes a path fromnegative battery 663, through the upper winding of relay 6 52, toparmature of relay 661, and then over the inner bottom armature of relay66! to positive battery 66!} to maintain a closed circuit condition.

At the same time, the operation of the top armature of relay 63l alsocloses a path for current to pass from grounded battery 665, through thewinding of relay 660, over the top armature of relay B31, and then overthe operated outer bottom armature of relay 563 to ground 636 therebyenergizing relay 660 which operates its armatures. The operation of theinner bottom armature of relay 66f] switches the ring side of thecalling subscribers loop circuit to the armature of relay i562 and thenthrough the monitoring teletypewriter 6&2 to the ring terminal ofrepeater 663. The operation of the top armature of relay 68B switchesthe tip side of the calling subscribers loop circuit to conductor 680leading to the tip terminal of repeater 603. This serves to switch thesubscribers loop to the monitoring to ground 628.

teletypewriter 602' on a two-way basis and in series with the main line604.

The operation of the outer bottom armature of relay GSB'completes anauxiliary locking-up circuit for relays B29 and BIB from battery 625,through the windings of relays 629 and (H8, over the top armature ofrelay 629, over the outer bottom .armature of relay 66B, and then overthe armature of relay 621 to ground 628 for a purpose to be explainedhereinafter.

The calling subscriber at station lfll now transmits the proper stationselecting signal to effect the energization of relays similar to relays631, 629, 629, 618, 665, and '66! at the central ofiice serving thecalled station. This connects the called subscribers loop into thesystem on a twoway basis ready for communication. If desired, othersubscribers stations may be connected into a conference connection in amanner similar to that described above.

After the desired stations are connected, the calling subscribertransmits the go ahead signal, such as C, which effects the closure ofthe C pullbar contact to close the energizing cir-' cuit for relay 63 1.Relay 634 operates its armatures, the inner armature opening thelocking-up circuit for relay 633 which releases its armatures to openthe path to relay 621. These same functions are performed by all of themonitoring teletypewriters in the system. This go ahead signal alsoefiects the energization of relay I33 to,

extinguish the guard lamp l2 lat the calling subscribers station lfil.The operation of the outer armature of relay 634 does not cause relays629 and BIS to release their armatures because they remain locked upover their auxiliary locking-up circuit which extends from battery 625through the windings of relays 629 and M8, over the top armature ofrelay 829, outer bottom armature of relay 650, and then over thearmature of relay 621 to ground 628. The system is thus placed in thecondition for communication to take place after which the communicativeconnection may be discontinued in a manner similar to that describedabove.

Privacy is assured because none of the loops extending from thesubscribers stations can be placed on a two-way basis until the signalsassigned for selecting them have been transmitted. Consequently, it isimpossible for message signals now passing over the system to berecorded by the teletypewriters at the subscribers stations notconnected into this particular communication connection.

In the event that a start key at a subscribers station has been operatedaccidentally or through error, such operation would energize relayssimilar to relays 629 and 558 which would operate their armatures andlock up over the outer armature of relay 634 and armature of relay 621to ground 628. As was described above, this causes negative current toflow over the tip side of the subscribers loop and positive current overthe ring side. In response to the positive current in the ring circuit,the subscribers relay similar to relay I24, moves its armature to itsmarking contact to energize relays I31] and I2! which operate theirarmatures and lock up over a circuit including the auxiliary stop keyI29 to start the subscribers teletypewriter motor, ring his bell brieflyand light his busy lamp.

This subscribers motor will now run until the subscriber at this.station realizes his motor is running for no useful purpose. Thesubscriber should then manually open his auxiliary stop key "If thisstation were tioned above for turesrjThis will effect the energizationof a re-,

lay corresponding torelay 660 which will operate its armatures to closethe auxiliary lockingup circuit for-relays B29and BIB extending frombattery 625, through the windings of relays 629 and fi [8, over the toparmature of relay 629, outer bottom armature-of relay 660, and then overthe armatureof relay-621 to ground 628. The station' will thus beconditioned for communication. not selected by the calling subscriber,'thenthe operation of the "go ahead signal would cause the relay 634 tooperate its armatures and, since the relay 66!) associated with thisparticular subscriber would not have been operated at this time, theoperation of the outer armature ofrelay 634 would open the locking-upcircuit ofrelays 629 and M8. However, relay620 remains locked up" overthe armature of relay 621 to' ground 67.8." This causes current to flowin the subscribers loop in a direction which is the reverse of thenormal marking currentas was described aboveQ If the subscribersteletypewriter shouldbe provided with a polar line relay, this reverseloop current would cause his teletypewriter-to run open. l

It is to be understood that the invention is not limited to the useofthe particular letters menperforming switching operations but that.various other letters and combinations of lettersmay be employediorthis purpose. It is be further understood that various modifications maybe made in the apparatus and circuits shown in the drawingswithoutdeparting from the scope of the invention which is to be limited only bythe claims appended hereto.

, What isclaimed is: r

r 1'. A teletypewriter switching systemcomprisingin combination acalling subscribers station provided with: a teletypewriter fortransmitting permutation code signals, a plurality of other subscribersstations each having a teletypewriter, ateletypewriter"central ofiice, atransmission circuitextending from each subscribers station tothecentral oflice for connecting the subscribers stations to, thecentral ofiice for communication,

switching means at the central ofii-ce for effecting the establishmentof acommunication connection fromthe calling subscribersteletypewriter-through the central oflice to a teletypewriter at any ofthe other subscribers stations, said switching means including aplurality of coning combination a a switching system compris- -callingsubscribers station provided with an indicator and a teletypewriter fortransmitting permutation code signals, a pinrality of other subscribersstations each having a teletypewriter, a teletypewriter centraloflice,za transmission circuit extending from each subscribers stationto the central oflice for connecting the subscribers stationsto thecentral oflice for communication, switching means for effect- 2. Ateletypewriter ing theestablishment of a communication connecticn fromthe calling subscribers station through the central ofiice to ateletypewriter at anyof the other subscribers stations, said switchingmeans including: a plurality of controlcontacts in the teletypewriter atthe. central office, operating means for selectively operating saidcontrol contacts in response to certain prease signedpermutationcodesignals transmitted by the teletypewriter at the callingstation,preparing means at thecentral officejfor preparing said switching meansfor operation, control means; at the calling subscribers station foreffecting the operation of said preparatory means, and operating meansfor operating the indicator at the call ing subscribers station inresponse to the operation of the preparatory means at the centralofiice. l

3. A teletypewriter switching system compris ing in combination acalling subscribersstation provided with a. teletypewriter fortransmitting permutation code signals, a pluralityof other subscribersstations eachhaving a busy lamp and a teletypewriter, ateletypewritercentral Office, a transmission circuit extending from eachsubscribers station to thecentral oflice for connecting the subscribersstations to the central ofiice for communication, switching means fortrol contacts in the teletypewriter at the central office, said controlcontacts in response to certain preassigned permutation code'signalstransmitted by the, teletypewriter at the calling station, conditioningmeans at the calling station for conditioningitffor communicativepurposes, said conditioningmeans including'a plurality of controlcontacts in the teletypewriter at the calling station, andinstrumentalities in the teletypewriter at the said control contacts inresponse to the transmission of some of said certainpreassignedpermutation code signals.

operating means for selectivelyoperating calling station for selectivelyoperating eifectingthe selective connection of the calling subscriberfsstationthrough the central oflice to any selected subscribers station,operating means forselectively operating the switching means in responsetocertain preassigned permutation code signals transmitted, by thecalling station, and means for illuminating the busy lamp in at leasteach of the unselectedsubscribers stations in response to thetransmission of at least one of said certain preassigned permutationvcode signals by the teletypewriterat the, calling'station. Q

4. A teletypewriter switching system comprising in combination a callingsubscribers station provided witha teletypewriter for transmittingpermutation code signals, a plurality of other subscribers stations,each having a teletypewriter and a motor with a start key for eflectingthe starting of the motor thereat, a-teletypewriter central oilice, atransmission circuit extending from each subscribers station .to thecentral office for connecting the subscribers stations to the centralOfiiCB for communication, switching means for eifecting the selectiveconnection of thecalling subscribers station through the central, ofiiceto any selected subscribers station, operating means for selectivelyoperating the switching means in response to certain preassignedpermutation code signals transmitted by the calling station, and meansfor disabling the start keys at all of the subscribers stations otherthan the calling subscribers station in response to the transmissionoiat least one of said certain preassigned permutation code signalsbytheteletypewriter at the calling station.

5. A communication system comprising in combination a plurality ofsubscribers"stations each provided with a teletypewriter fortransmitting permutation code signals, each of said stations also havinga motor for operating the teletypewriter thereat, local motor controlmeans at each station for starting the motor thereat, a central ofiicehaving a teletypewriter, each station having a transmission circuitextending to the central ofiice, a plurality of control contacts mountedin the teletypewriter at the central oifice, means for selectivelyoperating said control contacts in response to preassigned permutationcode signals transmitted from a teletypewriter at any of the stations,control means at the central oflice for preventing the operation of thelocal motor control means at all of the subscribers stations but onefrom being effective, and means for operating said control means inresponse to the operation of certain of said control contacts.

6. A communication system comprising in combination a plurality ofsubscribers stations each provided with an indicator and ateletypewriter for transmitting permutation code signals, a centraloi'lice having a teletypewriter, each station having a transmissioncircuit extending to the central office, a plurality of control contactsmounted in the teletypewriter at the central ofi'ice, means forselectively operating said control contacts in response to preassignedpermutation code signals transmitted from a teletypewriter at any of thestations, control means at the central ofiice for effecting theoperation of the indicators at all of the subscribers stations but one,and means for operating said control means in response to the operationof certain of said control contacts.

'I. A communication system comprising in combination a first group ofsubscribers teletypewriter stations, a first teletypewriter centraloflice local to the first group of stations, a second group ofsubscribers teletypewriter stations, a second teletypewriter centraloffice which is local to the second group of stations, each station ineach group having a transmission 100p extending to its respective localcentral oflice, means for causmg each of said transmission loops to beon a one-way basis the direction being from each subscribers station toits local central ofiice, a main transmission channel extending from onecentral office to the other central oflice, each subscribers stationhaving a motor for running its teletypewriter, local motor control meansat each station for starting the motor thereat for permitting thetransmission of permutation code signals from a subscribers station toits central office, a plurality of control contacts mounted in each ofsaid teletypewriters, means for selectively operating the contacts inthe teletypewriter at a subscribers station and in the teletypewriter atits local central office in response to certain permutation code signalstransmitted from the particular subscribers teletypewriter to theteletypewriter at its local central office, and means for converting asubscribers loop to a two-way basis in response to the operation ofcertain of the contacts in the teletypewriter at the central ofiicelocal to the particular subscribers station.

8. A communication system comprising in combination a first group ofsubscribers teletypewriter stations, a first teletypewriter centraloffice local to the first group of stations, a second group ofsubscribers teletypewriter stations, at second teletypewriter centraloffice which is local to the second group of stations, each station ineach group having a transmission loop extending to its respective localcentral oflice, means for causing each of said transmission loops to beon a one-v way basis the direction being from each subscribers stationto its local central office, a main transmission channel extending fromone central ofiice to the other central ofiice, each subscribers stationhaving a motor for running its teletypewriter, local motor control meansat each station for starting the motor thereat for permitting thetransmission of permutation code signals from a subscribers station toits central ofifice, a plurality of control contacts mounted in each ofsaid teletypewriters, means for selectively operating the contacts inthe teletypewriter at a subscribers station and in the teletypewriter atits local central office in response to certain permutation code signalstransmitted from the particular subscribers teletypewriter to theteletypewriter at its local central oflice, means for converting asubscribers loop to a two-way basis in response to the operation ofcertain of the contacts in the teletypewriter at the central oflicelocal to the particular subscribers station, and means for enabling asubscriber at one station to prevent the loops extending from the othersubscribers stations to their respective local offices from beingconverted to a two-way basis.

9. A communication system including in combination a teletypewritercentral oflice, a plurality of subscribers stations each having acommunication loop extending to the central office, each of saidsubscribers stations also having a teletypewriter for transmittingpermutation code signals over its respective communication loop to thecentral ofiice, said central ofiice having means for normally placingeach of said communication loops on a one-way basis the direction beingfrom each subscribers station to the central ofilce, said central officealso having control means for Selectively converting anylof saidcommunication loops to a two-way basis, and operating means forselectively operating said control means in response to the transmissionof at least one'preassigned permutation code signal by a telety'pewriterat one of said subscribers stations over its respective communicationloop to the central office. 4

10. A communication system including in combination a teletypewritercentral ofiice, a plurality of subscribers stations each having acommunication loop extending to the central office, each of saidsubscribers stations also having a teletypewriter for transmittingpermutation code signals over its respective communication loop to thecentral oflice, said central ofiice having means for normally placingeach of said communication loops on a one-way basis the direction beingfrom each subscribers station to the central ofiice, said central officealso having control means for selectively converting any of saidcommunication loops to a two-way basis, operating means for operatingsaid control means to convert any one of said communication loopsleading to a, subscribers station to a two-way basis in response to thetransmission of at least one preassigned permutation code signal by theteletypewriter at that subscribers station over its communication loopto the central office, and means for preventing any of the othercommunication loops being converted to a two-way basis by means otherthan in response to at least one other preassigned permutation codesignal transmitted by the teletypewriter at that subscribers stationwhich has its loop converted to a two-way basis.

11. A communication system including in combination a teletypewritercentral oflice, a plurality t of subscribers stations each having acommunication loop extending to the central ofiice, each of saidsubscribers stations also having a teletypewriter for transmittingpermutation code signals over its respective communication loop to thecentral ofiice, said central oifice having means for normally placingeach of said communication loops on a one-way basis the direction beingfrom each subscribers station to the central ofiice, said central ofiicealso having control means for selectively converting any of saidcommunicationloops to a two-way basis, operating means for operatingsaid control means to convert a first communication loop leading to afirst subscribers station to a two-way basis in response to thetransmission of at least a first preassigned permutation code signalscribers station over said first communication loop to the centralofiice; and means for operating said control means to convert a, secondcommunication loop leading toa second subscribers station to a two-waybasis in response to the transmission of at least a second preassignedpermutation code signal by the teletypewriter at said first subscribersstation over said first communication loop converted to a two-way basis;

12; A communication system including in combination ateletypewriter'central ofiice, a plurality of subscribers stations eachhaving a communication loop extending to the central office, each ofsaid subscribers stations also having a teletypewriter for transmittingpermutation code signals over its respective communication loop to thecentral oifice, said central office having means for normally placingeach of said communication loops on a one-way basis the direction beingfrom each subscribers station to the central ofiice, said central ofiicealso having control means for selectively'converting any of saidcommunication loops to a two-way basis, operating means for operatingsaid control means to convert a first communication loop leading to afirst subscribers station to a tWO-WaY baSlS in response to thetransmission of at least a first preassigned permutation code signal bythe teletypewriter at said first subscribers station over said firstcommunication loop to the central oiiice, means for operating saidcontrol means to convert a second communication loop leading to a secondsubscribers station to a two-way basis in response to the secondpreassigned permutation code signal by the teletypewriter at said firstsubscribers station over said first communication 100p converted to atwo-way basis, and means for restoring said first and secondcommunication loops to a oneway basis in response to the transmission ofat least a third preassigned permutation code signal by one of theteletypewriters at said first and second subscribers station. a g

13. A communication system comprising in combination a first group ofsubscribers stations each having a teletypewriter for transmittingpermutation code signals, a first central ofi'ice having ateletypewriter local to the first group of stations, a second group ofsubscribers stations each having a teletypewriter for transmittingpermutation code signals, a second central oifice having ateletypewriter which is local to the second group of stations, eachstation in each group having a transmission loop extending to itsrespective local central ofiice, means for causlng each of saidtransmission loops to be one a by the teletypewriter at said first sub--transmission of at least a signals from a subscribers station to itscentral n one-way basis the direction being from each sublocal centraloflice, a main extending from onecentral e to the other central ofiice,each subscribers station having a motor for running its teletypewriter,local motor control means at each station for starting the motor thereatfor operating its teletypewriterfor transmitting permutation codeplurality of control contacts mounted in said teletypewriters, means forselectively operating the contacts in the teletypewriter at a lsubscribers station and in the teletypewriter at its local centraloffice in response to certain preassigned permutation code signalstransmitted from the particular subscribers teletypewriter to localcentral office, conthe teletypewriter at its trol means for converting afirst subscribers loop to a two-way basis in response to the operationof at least one of said control contacts in the teletypewriter at thecentral ofiice local to the first subscribers station, and means forconverting a second subscribers p to a two-way basis in response to thetransmission of at least one preassigned permutation code signaltransmitted subscribers station over said first subscribers loopconverted to a two-way basis.

14. A communication system comprising in RUSSELL J. AN SPACH.

